DE2032174B2 - Process for the production of flame-resistant and thermoformable rigid foams containing biuret groups and urethane groups - Google Patents

Description

CO-N

R-- NCO

in which R has the meaning given above and η is an integer from 1 to 5, used in monomeric polyisocyanates in which the proportion of biuret-containing polyisocyanates with more than 3 isocyanate groups, based on the total amount of biuret polyisocyanates, is at least 20 percent by weight and 0.03 to 5 percent by weight of the emulsifiers were also used in their production.

3. Process according to Claims 1 and 2, characterized in that the polyether is used Rigid foams containing urethane groups, which are obtained by reacting polyisocyanates m, '; active Obtained polyols containing hydrogen atoms

ι ο are widely used, e.g. B. in the field insulation and the production of structural elements. The uses of the foamed Polyurethanes is, however, due to their flammability when exposed to high temperatures and / or Fire limited.

It is known that foams containing urethane groups which have flame-retardant properties, from compounds with active hydrogen atoms, preferably polyols, polyisocyanates, water and / or

'() other propellants, in the presence of emulsifiers, Manufacture auxiliaries and catalysts as well as flame-retardant additives. Serve as polyols usually a functionality of at least three and an OH number > 300 having

. '■> Polyether and polyester polyols.

Compounds of phosphorus, halogens, antimony, Bismuth, boron and, to a certain extent, nitrogen have become known. The flame retardant additives

ίο can be divided into those identified by the The presence of functional groups can be incorporated into the foam structure with and into those that due to the lack of such groupings, they can only be incorporated and more than plasticizers or

ii Fillers work (see Chapter 2.3.10 "Flame-Retardant Substances", Kunststoff-Handbuch, Vieweg-Höchtlen, Volume VIl, Polyurethane, Carl-Hanser-Verlag, Munich 1966).
The introduction of such lamb-retardant compounds

4 (i fertilize in foams containing urethane groups with low density and large surface often causes a loss of desirable physical properties, such as compressive strength and thermal stability, which limits the application of the foam

4) will. In addition, halogen-containing flame retardants tend to be at higher temperatures to split off hydrogen halide. Since the foaming process is high Temperatures escape, the use of such flame retardants is further restricted.

> <> The use of flame retardant additives can also lead to a severe disruption of the internal cell structures, leading to the formation of a coarse cell structure and / or lead to a collapse of the foam. An effective fire protection from

ü Urethane foams as opposed to compact ones Polyurethanes is also difficult insofar as a desired distribution of the additive at the phase interfaces "Gas / Solid" is not possible due to the composition of the foam mixture. It is also

ho pointed out that the effective fire protection a polyurethane foam not just a simple function of adding various fire retardants Means is.

Surprisingly, it has now been found that

h> flame-retardant, biuret and urethane groups Rigid foams with the desired physical properties can be obtained if one special Polyisocyanates with special linear polyethers,

which have only two hydroxyl groups and a molecular weight of 200 to 800.

According to the invention, solutions of polyisocyanates containing biuret groups in monomeric polyisocyanates, in the preparation of which 0.03 to 5 percent by weight of emulsifiers with OH, amino, amido, COOH, SH or urethane groups were also used, are used as special polyisocyanates. The achievement of high flame resistance with foams containing urethane groups means that they are designated as self-extinguishing according to ASTM method D 1692-67 T, but also partially achieve the "flame retardant" standard according to DIN 4102.

The polyisocyanates containing biuret groups have an increased NCO functionality, i. H. she have significant proportions of compounds with 3, 4, 5 and more NCO groups per molecule.

When using the method according to the invention, there are significant technical advantages:

The solutions to be used according to the invention of polyisocyanates containing biuret groups in monomeric polyisocyanates are liquids at room temperature, the viscosity of which varies from potash can be set at will. These higher viscosity polyisocyanates can be used with the invention Mix the polyethers used and the other foam components very well and quickly. Fs stable foams are obtained which have no tendency to collapse when they are formed show and have a fine, regularly formed cell structure.

The invention thus provides a method for producing flame-resistant and thermoformable materials Rigid foams containing biuret groups and urethane groups by implementing solutions of polyisocyanates containing biuret groups in monomeric polyisocyanates with hydroxyl groups containing polyethers, water and / or other blowing agents, catalysts, emulsifiers and optionally other aids. The process is characterized in that the hydroxyl groups Polyethers comprising linear polyethers with two hydroxyl groups and a molecular weight of 200 up to 800, which is achieved by reacting an ε-omatic compound with two active hydrogen atoms with alkylene oxides or mixtures thereof, and which are optionally proportionally containing trifunctional polyethers with an OH number of 300 to 600, and one as solutions of Polyisocyanates containing biuret groups in monomeric polyisocyanates are used in their Manufacture 0.03 to 5 percent by weight of emulsifiers with OH-, amino-, amido-, COOH-, SH- or has also used urethane groupings.

From FR-PS 15 33 695 is already a method for Manufacture of flame-retardant rigid polyurethane foams known in which one biuret group containing polyisocyanate. which is dissolved in monomeric polyisocyanates, with an active hydrogen atom containing compound in the presence of water and / or another blowing agent. According to the invention however, those polyisocyanates are selected, soft chemically bound emulsifiers contain, and those polyethers that are linear and relatively low molecular weight and by reaction an aromatic compound having two active hydrogen atoms with alkylene oxides or mixtures of which have been obtained. The result of this selection is hard, self-extinguishing Polyurethane foams, which are usually thermally deformable.

The subject of the older DE-OS 19 24 302 is on ", the manufacture of flexible polyurethane foams using biuret groups Directed polyisocyanates, while hard, thermoplastically deformable foams obtained according to the invention only the special ίο polyethers are used for their production.

The two hydroxyl groups preferably used in the process according to the invention Polyethers have an OH number of 140 to 560, and in them at least 5% of the OH groups present are > pen primary hydroxyl groups. The primary OH group determination is carried out according to Gordon Hanna and Sidney Siggia, Journal Polymer Science, Vol. 56, pp. 297-304 (1962). The polyethers to be used according to the invention are obtained by reaction > u one containing two active hydrogen atoms aromatic compound with alkylene oxides, such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide or Epichlorohydrin, or mixtures of these alkylene oxides, the terminal primary OH groups :> pen ζ. 3. through subsequent implementation of the polyethers can be obtained with ethylene oxide.

Serve as the starting material for the production of these polyethers

Resorcinol, hydroquinone,
jo 3-hydroxy-2-naphthol,

2,2-bis (p-hydroxyphenyl) propane,
Bis (p-hydroxyphenyl) methane,
Aniline, toluidine,

Bis-N, N'-alkyl-diphen / lmethanediamine and
ti bis-N.N'-alkyl-toluenediamine.

The polyethers to be used according to the invention are preferably also used with ethylene oxide built up. The polyethers can optionally also be proportionally trifunctional polyethers with an OH number from 300 to 600 included. Preferred here are an alkoxylation product of glycerol, trimethylolpropane, Hexanetriol, ammonia and ethanolamine.

In the method according to the invention, all solutions of biuret groups can generally be present-4-, use the polyisocyanates in monomeric polyisocyanates, the preparation of which is 0.03 to 5 Percentage by weight of emulsifiers with OH, amino, amido, COOH, SH or urethane groups has also used.

, ο However, 1 to 85% strength by weight solutions are preferred of polyisocyanates containing biuret groups Jer general formula

O
OCN - R N - CNR NCO

X N R.

NCO
in the

Pure Ci-Cm-alkylene radical, C5-C | _0- cycloalkylene radical, C7-Ci2-aralkylene radical or Cfc-d
and

X is hydrogen or a group of the general formula

CO N

R NCO

in which R has the meaning given above and η is an integer from I to 5, in monomeric polyisocyanates in which the proportion of biuret-containing polyisocyanates with more than 3 isocyanate groups, based on the total amount of biuret polyisoeyanate, is at least 20 % By weight and 0.03 to 5% by weight of the emulsifiers were also used in their production.

The preparation of polyisocyanates containing biuret groups is known per se, e.g. B. from GB-PS 8 89 050 or from DE-PS 11 0! 394. She can /.B. by reacting monomeric polyisocyanates with water, formic acid, hydrogen sulfide or tertiary Alcohols.

The polyisocyanates containing biuret groups used according to the invention are preferably made from monomeric polyisocyanates prepared by reaction with water, using a non-ionic emulsifier. The monomeric polyisocyanates are aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic, di- and / or higher polyisocyanates in question, z. B.

1,4-tetramethylene diisocyanate,

l.e-hexamethylene diisocyanate.

Cyclohexane-1,3- and 1,4-diisocyanate.

1 -ivicthyl-cyclohexane ^ - and

^, b-diisoeyanat
or mixtures of these isomers,

m- and p-xylylene diisocyanate.

2,4- and 2,6-tolylene diisocyanate
and mixtures of these isomers.

Diphenylmethane-4,4'-diisocyanate,

Naphthalene-1.S-diisocyanate.

Triphenylmethane-4,4 ', 4 "-tnisocyanate,

Isophorone diisocyanate,

Polyphenyl polymethylene polyisocyanates,
such as are obtained by aniline-formaldehyde condensation and subsequent phosgenation, and polyisocyanates containing carbodiimide-isocyanate adducts, such as are obtained, for example, according to DE-PS 10 92 007.

Furthermore, polyisocyanates containing biuret groups are suitable which are obtained by reacting diisocyanates with primary aromatic diamines of weakened nucleophilicity or with aromatic diamines containing two secondary amino groups, tetraisocyanates of the following general formula preferably being formed:

X X

N-

C = O

OCN-R —N

R 'N

O = C

N-R-NCO

C = O O = C

! I.

HN-R-NCO

OCN-R -NH
in the
R 'is a divalent aromatic radical

R is a divalent aliphatic, cycloaliphatic, araliphatic and aromatic radical and

X is an alkyl grouping or hydrogen or the grouping

CO
HN R NCO

means.

For the preparation of the polyisocyanates containing biuret groups to be used in accordance with the invention in the form of solutions in monomeric polyisocyanates, however, polyisocyanates of a higher molecular weight can also be used, e.g. B. polyisocyanates which contain isocyanurate groups and / or irethane groups and / or ester groups and / or ether groups and / or amul ^ rnnnrn nnrj / nrVr I! Retd! On ^a rU '?'? Cn and / or carbodiimide groups. It is Z. B. possible to implement the above-mentioned monomeric polyisocyanates with insufficient amounts of compounds with reactive hydrogen atoms and the resulting isocyanate groups containing pre-adducts z. B. to convert polyisocyanates containing biuret groups in the presence of the emulsifiers by reaction with water or formic acid. Compounds containing reactive hydrogen atoms suitable for this purpose are ι. B. aliphatic, cycloaliphatic, araliphatic or aromatic compounds which, for. B. OH-. SH- COOH-. NH, -. NHR-. (R = alkyl or aryl) groups. Compounds containing hydroxyl groups are preferred. Examples are: water. Methanol. Ethanol. Butanol. Octanol. Dodecyl alcohol, allyl alcohol. Cyclohexanol. Phenol. Cresol, ethylene glycol. Butanediol- (1.4). Hexanediol- (l.6). Diethylene glycol, trimethylol propane. Ethanolamine. Dihydroxyethyl-oleylamide, dihydroxyethylsiearylamide and tetrahydroxyethyl-ethylenediamine. Hydroxyl-containing polyesters or polyesteramides can also be used as compounds with reactive hydrogen atoms, e.g. B. those with molecular weights of 200 to 3000, which are known in a manner by reacting polycarboxylic acid, such as adipic acid, with polyhydric alcohols, such as butanediol (1,4) and / or polyamines, such as hexamethylenediamine ^ 1.6) and / or amino alcohols such as ethanolamine. Likewise, adducts of alkylene oxides, such as. B. ethylene oxide. Propylene oxide, butylene oxide, styrene oxide or epichlorohydrin, on the aforementioned low molecular weight compounds with reactive hydrogen atoms or on water with molecular weights of, as a rule, from 200 to 1000 can be used.

Polyisocyanates already of a higher molecular nature, the Can be used to prepare the biuret-containing polyisocyanates are also those obtained by polymerizing the aforementioned monomeric polyisocyanates to give isocyanurate groups containing polyisocyanates have been obtained. The polymerization of monomeric polyisocyanates too Polyisocyanates containing isocyanurate groups can ζ. B. according to the teaching of DE-PS 9 51 168, 9 54 376 and 11 12 285.

According to the invention to be used with advantage polyisocyanates are solutions of Biuretpoiyisocyanaten, obtained by reacting 2,4- and / or 2,6-ToIuylendiisoeyanat with water or formic acid in 2,4- and / or 2,6-toluene diisocyanate

Solutions of biuret polyisocyanates, which have been obtained by reacting 4,4'-diphenylmethane diisocyanate and / or its isomers with arisenic acid or water, in 4'-diphenylmethane diisocyanate and / or its isons or solutions of biuret polyisocyanates , which are obtained by reacting 2,4- and / or> - Jer 2,6-toluylene diisocyanate with formic acid or water, in a mixture of 2,4- and / or 2,6-toluene diisocyanate and 4,4'-Diphenylmethane diisocyanate> ld / orcr.:n isomers. A polyisocyanate is also preferred. which is a solution of a polyisocyanate containing biuret, which is produced by reacting a polyisocyanate mixture. represented by Λ: obtained ilin-Formaldchyd-Kondensaiion, followed by phosgenation, mn formic acid and water has been prepared, in a ^Po: isocyanate represented by

Phosgenation produced. This according to the invention The 'olyisocyanates used are, as described, including from 0.03 to 5 Percent by weight, preferably 0.1 to 2 percent by weight, on emulsifiers with OH, amino, amido, C DOH, SH or uretha groups been, these emulsifiers are chemically bound to the polyisocyanates.

Preferred reactive emulsifiers for preparing the biuret polyisocyanate systems which can be used according to the invention are, for example, hydroxyl-containing Oley alcohol polyglycol ethers, castor oil polyethylene glycol ethers, Isononylphenol polyglycol ether, 3-benzyl-4-hydroxy-biphenyl polyglycol ether, higher molecular weight polyglycol ethers with an average molecular weight of 2000 with one n-dodecyl and one terminal OH group, emulsifiers containing amino end groups of the aforementioned constitution, as they are by Cyanoethylation and subsequent hydrogenation of the aforementioned emulsifiers can be obtained. the various ammonium salts of oleic acids and long-chain fatty acids and their salts with primary ones and secondary amines are also eminently suitable, as they are in the submitted polyisocyanates dissociate, the amines react as ureas and the longer-chain carboxylic acids in isocyanatoacy! - arnide derivatives are converted.

In general, the polyisocyanates containing biuret groups to be used according to the invention are solid or resinous products or more or less viscous oils at room temperature. They have a surprisingly high solubility in monomeric polyisocyanates. The solutions of polyisocyanates containing biuret groups to be used according to the invention also prove to be very compatible with the components to be used for foam production, especially with the linear polyethers containing hydroxyl groups to be used according to the invention.

To prepare the solutions to be used according to the invention of the polyisocyanates containing biuret groups in the monomeric polyisocyanates in many cases the polyisocyanates containing biuret groups are first produced and then the monomeric ones Dissolved polyisocyanates A preferred procedure, however, consists in preparing the polyisocyanate containing biuret groups in the solvent (monomeric polyisocyanate) to be carried out yourself, with the addition of further monomeric Polyisocyanates the desired concentration of

Can produce polyisocyanate solution. Usually will I to 85% by weight solutions of polyisocyanates containing biuret groups in monomeric polyisocyanates use.

The foam production can be carried out by the methods known per se, for. B. after the so-called »One-shotw process.

The amounts of polyisocyanate solutions containing biuret polyisocyanates used should as a rule be equivalent to the sum of OH groups present. Under certain circumstances, however, in the case of the invention In the process, an approx. 50% excess isocyanate may be advantageous. I5ci only use the linear polyether it is advantageous for the physical property profile of the foam, the Reaction mixture 1 to 3 parts ·, · water, based on 100 Parts of polyether to be attached. In cases where the

r4..n ». _r . · Wt r. *. ~~ - —Ι- ~ T ~ ~ .. '. L. -; * * - 1 ..— .. ". I.". I · ■ O.

UUIIg vOll tfd3.lt! ai3 I I (.IU [[[I [I (. [UIICI WUII) LIII IM, I d IJ [ the same effect can also be achieved by admixing 20 to 50 parts of a trifunctional polyether with the OH number Achieve from 300 to 600.

There is also the possibility, according to the diagram, to achieve an optimal physical Property profile of the foams, the necessary amount of water gradually through trifunctional polyethers to replace.

In the diagram, the linear polyether is a propylene oxide polyether started on bisethoxylated bisphenol A. the OH number 200, which is terminally modified with 13% ethylene oxide. The trifunctional polyether is an ethylene oxide polyether of the OH number based on trimethylolpropane! 533

The occurring in the process according to the invention The flame retardancy of the foams can be increased by adding flame retardant substances such as organic Phosphorus, halogen, antimony, bismuth and sulfur compounds are still to be improved.

Foam production using the “one-shot” process takes place at room temperature or higher Temperature by simply mixing the polyisocyanate solutions with the polyethers, water and / or other blowing agents, optionally emulsifiers and auxiliaries. Here one uses siel, advantageously machine facilities, such as. B. in FR PS Ϊ0 74 7Ί3 are described, or procedures as described in DE-PS 8 81 881 are described.

As propellants, those known per se come into question, for. B. low-boiling organic chlorofluorocarbons, such as monofluorotrichloromethane or difluorodichloromethane.

As emulsifiers for foam production, reference is made to ethylene oxide or ethylene oxide-propylene oxide adducts with substances containing hydrophobic hydroxyl, hydroxyalkyl or amino groups or amido groups.

Amines and / or silaamines are used as catalysts or hexahydrotriazines are used, optionally in combination with organic metal compounds.

Compounds known for the production of polyurethane foams can be used as amines be used, for example

Dimethylbenzylamine, N-ethylmorpholine, Triethylenediamine, Dimethylpiperazine,

1,2-dimethylimidazoI,

Dimethylaminoethanol, Diethanolamine,

Triethanolamine,
Diethylaminoethanol and
N, N, N ', N'-tetramethyl-1,3-butanediamine;
Silaaniine are silicon compounds that contain carbon-silicon bonds, such as those found in e.g. B. in DE-PS 29 290 are described. Examples are: 2,2,4-trimethyl-2-silamorpholine,
U-Diethylaminomethyl-tetramethyldisiloxane.

However, reference should also be made to nitrogenous bases and alkalis or alkali phenolates. The possibly organic metal compounds used in combination with amines, silaamines and hexahydrotriazines are preferred organic tin compounds, e.g. B. tin (II) octoate or dibutyltin dilaurate.

Additives to regulate pore size and cell structure can be used as well as fillers, flame-retardant additives, dyes or plasticizers of the type known per se.

The foams obtained are widely used, for. B. in construction as building panels, sandwich elements, Ceilings and parapet panels, for thermal insulation in refrigerated cabinets, refrigerated warehouses, refrigerated trucks and Refrigerated containers, also in road and rail construction, for technical insulation of pipes and of Tank farms, in shipbuilding and as packaging material for protection against impacts. It is also possible, Manufacture molded polyurethane foams with a compact surface and a cellular core. There foams with a thermoplastic character are also obtained by the process according to the invention If necessary, a shaping in the heat can also be carried out on the finished foam.

example 1

Preparation of a solution of biuret groups

containing polyisocyanates in monomers

Polyisocyanates

a) In 1,050 g of a mixture of 80% 2,4- and 20% 2,6-tolylene diisocyanate, in the above 2 g of a Rizinuspolyethylenglykolethers an OH number of 50 were stirred, at 60 ³ C with stirring, within 30 minutes 21 g of H2O were added dropwise. The deposited precipitate dissolves during the subsequent heating to 170 ° C. After maintaining this temperature for 3 hours, the mixture is rapidly cooled to room temperature. The product obtained in this way has a viscosity of 5500 cP / 25 ° C. with an NCO content of 33.2%.

Method according to the invention

b) A mixture of 100 g of a propylene polyether started on bisethoxylated bisphenol A and containing 13% ethylene oxide at the end (OH number 196, viscosity 2600 cP / 25 ° C), 2 g H ₂ 0.0.4 g endo-ethylene piperazine and 25 g of monofluorotrichloromethane are intensively stirred with 122 g of the biuret polyisocyanate solution prepared according to la). A hard polyurethane foam which is self-extinguishing in accordance with ASTM D 1692-67 T and has the following physical properties is obtained:

Volume weight: 30 kg / m ³ Compressive strength: 1.9 kp / cm ² Heat bending strength: 130 ° C

The foam shows no change in dimension at -30 ⁰ C and + 100 ⁰ C for 5 hours.

Example 2

A mixture of 76 g of the polyether used in Example Ib), 24 g of an ethylene oxide polyether started on trimethylolpropane and having an OH number of 533, 1 g of H2O, 0.4 g of endo-ethylene piperazine and 35 g of monofluorotrichloromethane is prepared with 119 g of that according to la) Biuret polyisocyanate solution stirred intensively.

A according to ASTM D 1692-67 T is obtained self-extinguishing rigid polyurethane foam with the following mechanical properties:

Volume weight:

Compressive strength:

Thermal flexural strength:

24 kg / m '
1.1 kp / cm- '
130 ⁰ C

The foam shows no change in dimension at -30 ⁰ C and + IOO ^r C for 5 hours.

Example 3

A mixture of 60 g of the polyether used in Example 1 b), 40 g of one based on trimethylolpropane started ethylene oxide polyether of GH number 533, 0.3 g of endo-ethylene piperazine and 40 g of monofluorotrichloromethane is intensively stirred with 116 g of the biuret polyisocyanate solution prepared according to la). You get a self-extinguishing rigid polyurethane foam according to ASTM D 1692-67 T with the following mechanical Characteristics:

Volume weight:

Compressive strength:

Thermal bending strength:

28 kg / m ¹
1,2 kp / cm-12O ⁰ C

Example 4

100 g of a propylene oxide polyether started on bisethoxylated bisphenol A and terminated with 13% ethylene oxide was modified, an OH number of 266 and a viscosity of 13,000 cP / 25 ° C mixed with 1.5 g of water, 0.5 g of endo-ethylene piperazine and 30 g of monofluorotrichloromethane. The mix will mixed with 83 g of the biuret polyisocyanate solution prepared according to la). A according to ASTM D is obtained 1692-67 T self-extinguishing rigid polyurethane foam with the following mechanical properties:

Volume weight:

Compressive strength:

Thermal flexural strength:

21 kg / m>
1.1 kgf / cm ²
112 ⁰ C

The foam showed no dimensional change at +100 ⁰ C and at -30 ° C for 5 hours.

Example 5

A mixture of 84 g of a propylene oxide polyether started on aniline and containing 13% ethylene oxide at the end (OH number 242), 16 g of a propylene oxide polyether started on trimethylolpropane with OH number 530, 1.5 g H ₂ O, 0.5 g endo Ethylenepiperazine and 35 g of monofluorotrichloromethane are vigorously stirred with 130 g of the biuret polyisocyanate solution prepared according to la). A rigid polyurethane foam which is self-extinguishing according to ASTM D 1692-67 T and has the following mechanical properties is obtained:

Volume weight: Compressive strength: Thermal flexural strength:

31 kg / m ¹ 1.4 kp / cm ² 135 ° C

Il

Example 6

A mixture of 100 g of a propylene oxide polyether started on N, N-dimethyl-4,4'-diamino-diphenylmethane and containing 13% ethylene oxide at the end, with an OH number of 210, 2.5 g of H ₂ O, 0.3 g endo-ethylenepiperazine and 30 g of monofluorotrichloromethane are stirred intensively with 124 g of the biuret polyisocyanate solution prepared according to 1 a). A foam is obtained which is self-extinguishing in accordance with ASTM D 1692-67 T and has the following mechanical properties:

Volume weight: 25 kg / m ¹

Compressive strength: 1.1 kp / cm- '

Wärmebiegefestigkcit: 120 ⁰ C.

Example 7

Preparation of a solution of a biuret group

having polyisocyanate in monomers

Polyisocyanates

a) 1000 g of 4,4'-diisocyanatodiphenylmethane are stirred with 2.5 g of a castor polyethylene glycol ether with an OH number of 50 ^{at 50 ° C.} Afterward

15 g of H ₂ O are added dropwise with stirring. The suspension obtained is heated to 170 ° C. for 2 hours, during which the precipitate goes into solution.
A polyisocyanate which is liquid at room temperature and has an NCO content of 24.1% and a viscosity of 5700 cP at 25 ° C. is obtained.

Method according to the invention

A mixture of 100 g of the polyether used in Example Ib), 2.2 g of H ₂ O. 0.6 g of endo-ethylene piperazine and 30 g of monofluorotrichloromethane is vigorously stirred with 163 g of the biuret polyisocyanate solution prepared according to 7a). A rigid polyurethane foam which is self-extinguishing in accordance with ASTM D 1692-67 T and has the following mechanical properties is obtained:

Compressive strength:
Thermal flexural strength:

LI Kg / III '

1.2 kp / crn- ¹
95 ° C

About 1 cm thick panels made of this foam are flame retardant according to DIN 4102.

Claims (2)

Patent claims: 1. A process for the production of flame-retardant and thermoformable rigid foams containing biuret groups and urethane groups by reacting solutions of polyisocyanates containing biuret groups in monomeric polyisocyanates with polyethers containing hydroxyl groups, water and / or other blowing agents, catalysts, emulsifiers and optionally other auxiliaries, characterized in that one as hydroxyl-containing polyethers, linear polyethers with two hydroxyl groups and a molecular weight of 200 to 800, which have been obtained by reacting an aromatic compound containing two active hydrogen atoms with alkylene oxides or mixtures thereof, and the optionally proportionally trifunctional polyethers with an OH number of 300 to 600 contain, used, and solutions of polyisocyanates containing biuret groups in monomeric polyisocyanates are used in the preparation of which 0.03 to 5% by weight of emulsifiers with OH-, Amino, amido, COOH, SH or urethane _ö 'groupings has also used. 2. The method according to claim 1, characterized in that 1 to 85 percent by weight Solutions of polyisocyanates containing biuret groups and having the general formula ii
OC ¹ NRNCN- · -R- NCO O = -C X XN
i
R. NCO
in the Pure C, -do-alkylene radical, C -.- Cio-cycloalkylene radical, Cz-Cu-aralkylene radical or C _h -Cm-arylene radical and X is hydrogen or a group of the general formula one used in which at least 5% of the hydroxyl groups present are primary hydroxyl groups are.